This invention relates to providing a system for improved heat rejection. More particularly, this invention relates to providing a system for variable heat rejection in vehicles that experience highly varying thermal environments, highly varying heat loads, or both. Missions or vehicles that experience such variability in thermal conditions are common in space exploration and this variability causes a difficult thermal control challenge Maintaining thermal control is critical for the function of vehicle electronics as well as life-support systems for crewed vehicles. The thermal control system must maintain a relatively constant internal environment temperature, especially in the case of crewed vehicles, despite the vastly varying thermal conditions. However, radiator systems used for this thermal control are limited in their turn-down, or range of heat rejection capacity. This limitation, a function of the basic design limitations of the current state-of-the art, having a constant area, view factor, and emissivity, drives thermal control system design toward choices such as toxic fluids with low freezing points, complex controls, limited missions, and multi-loop systems which increase cost, complexity and mass.
High turn-down is of particular interest for deep space exploration, such as for travel to and exploration of other planets, where an exploration vehicle spends large periods of time in extreme cold when in transit, but operates in a hot or variable environment when orbiting or exploring such bodies. A variable heat rejection system with high turn-down can enable single-loop thermal control systems throughout such a mission, thereby significantly reducing complexity and mass of an exploration vehicle. High turn-down variable heat rejection also enables unique spacecraft power plants needed for that may not be in use continuously, and expands the potential range of modern space travel.
For the reasons above, The need for improved variable heat rejection in space exploration has informed the development of related variable heat rejection devices, including stagnating radiators (U.S. Pat. No. 9,109,843), mechanically louvered (U.S. Pat. No. 3,872,911) and MEMS louvred radiators (U.S. Pat. No. 6,538,796), electrostatically augmented radiative surfaces (U.S. Pat. No. 6,899,170), electrochromic radiators (U.S. Pat. No. 8,679,582), and pressure driven expandable radiators (U.S. Pat. No. 4,813,476). A higher turn-down than has been thus far achieved is needed though for deep space exploration, with projections that better than 12:1 turn-down is required for a Martian mission. Some projections suggest a turn-down of 100:1 may be needed for other deep space missions of the future.